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Measuring performance on SSD (Solid State Disk) drives and CacheCade

Understanding the best methods to test SSD and CacheCade devices to correctly observe the benefits of solid state storage might not be the easiest thing. So in this article we aim to provide guidance on the optimal performance specifications which can be applied generically to most of the performance testing tools.

For SSD and CacheCade:

Block-size: To measure IOPS, use a block-size which matches the disk sector size as this will give the highest count of efficient transactions. This value should be 4kb. Picking a smaller block-size will be inefficient as the whole 4k disk sector will still have to be read/written to; picking a larger block size won’t provide a valid measurement of IOPS.

Queue-depth: Provide at least 64 outstanding IO’s (also known as QD). Scale the queue-depth through 96, 128 and 256, re-running the test each time to see where the performance flattens off.

For SSD specifically:

Test file size: choose a test file size which will be bigger than the first-level cache. On a PERC H700 and H710 this is either 512MB or 1GB, on PERC H710P this is 1GB. Smaller file sizes will allow the controller to carry out all IO operations in cache, providing an invalid result.

For CacheCade specifically:

Cache warm-up: CacheCade caches read operations only. So you need to warm-up the cache by running the same benchmark to create significant numbers of reads from the test file before launching a performance test. The larger the data-set (test file), the longer the warm-up. Some performance tools such as fio in Linux provide a ramp-time option to allow for this.